There has rapidly been increased requirements for the development of a large capacity-information transmission along with the recent wide spread of personal computers and the internet. For this reason, it has been desired for the spread of the optical transmission, which can ensure a high transmission rate, even to the terminal information transmission devices such as personal computers. To realize this, it is necessary to mass-produce, at a low production cost, a small-sized optical transmission-reception module whose optical transmission and reception functions are united using a high quality optical waveguide or the like, for use in the optical interconnection.
As materials for preparing such an optical waveguide, there have been known, for instance, inorganic materials such as glass and semiconductor materials and various resins. When it is intended to prepare an optical waveguide using a resin, film-forming processes required can be conducted by coating and heating operations under the atmospheric pressure and accordingly, this method is quite advantageous in that devices and processes to be used are quite simple. Various kinds of resins have been known as those which permit the constitution of an optical waveguide and a clad layer and, in particular, polyimides have been expected as such materials because of their high glass transition points (Tg) and excellent heat resistance. When preparing the core and clad of such an optical waveguide using a polyamide resin, the resulting waveguide may ensure long-term reliability and it can withstand the soldering.
The conventional optical waveguide comprising such a core and a clad is formed on a thick substrate made of, for instance, an inorganic material such as glass or silicon or an organic material such as an acrylic resin and therefore, it is inferior in its flexibility. For this reason, it has been difficult to apply such a conventional optical waveguide to optical wire distribution and/or branching having good flexibility.
Thus, there have been prepared a polymeric optical waveguide film having flexibility, which simply comprises a core and a clad, both of which are made of polymer materials.
Such a flexible polymeric optical waveguide film has conventionally been prepared by applying a clad onto a thick substrate made of, for instance, an inorganic material such as glass or silicon or an organic material such as an acrylic resin; forming a core on the clad; applying a clad in such a manner that the core is completely covered with the same to thus form a polymeric optical waveguide film; and then removing the resulting waveguide film from the substrate.
However, if the adhesion between the substrate and the film is too weak, the film is often removed from the substrate during the course of the preparation thereof, while if the adhesion between them is too strong, the resulting film cannot easily be removed from the substrate. For this reason, there has been desired for the development of a method which can ensure a strong adhesive force between a substrate and a polymeric optical waveguide film during the course of the preparation thereof and which permits easy removal of the resulting film from the substrate. However, there has not conventionally been known any method which can satisfy the foregoing requirements.
As has been discussed above, the use of a fluorine atom-containing polyimide type resin would permit the preparation of an optical device excellent in optical characteristics as compared with those observed for an optical device obtained using an inorganic substance such as a glass material, while using simple processes. However, this method suffers from such a problem that defects are formed on the surface of the clad layer during the process for the production of the optical waveguide film and that the fluorine atom-containing polyimide resin film is sometimes peeled off from the substrate during producing the film due to a low adhesive force between the film and the substrate. Moreover, the fluorine atom-containing polyimide type resin shows insufficient resistance to solvent attack and therefore, problems arise, such that the method is considerably limited in solvents, which can be used in the step for washing the resulting film and that when using a commonly used solvent such as acetone, cracks are formed.